Personally, I have only used Dynamat Extreme because I have bought bulk packs off of Ebay. If you are trying to reduce road noise, check into MLV (mass-loaded vinyl) and CCF (Closed CEll Foam - neoprene).

What I did in my previous car (96 Buick Roadmaster) was to dynamat the exterior skin of the door, 1 layer of 1/4" neoprene on top of that. Then underneath the door panel (on the frame of the door) was 1 layer of dynamat and another layer of 1/4" neoprene. I did this to all 4 doors and it made a very noticeable difference in road noise (especially in the rain). I now have a roadmaster wagon and am awaiting some funding to do it again but this time I will use some MLV and some open cell foams where possible (dry areas only).

Depending on how far you want to go, dynamat has a 72 sq/ft mega pack shipped for under $300 on ebay (dynamat #10465)

Alot of updated info here:
http://sounddeadenershowdown.com/

I went with the HQ foam from here:
http://www.closedcellfoams.com/neoprene.html

A source for MLV:
http://www.cyber-bridge-marine.com/mass-barrier-1-8-4-5-ft-x-30.html